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Interaction of calcium ions with gastrin fragments of increasing chain length
Author(s) -
Peggion E.,
Foffani M. T.,
Wünsch E.,
Moroder L.,
Goodman M.,
Mammi S.
Publication year - 1986
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360250110
Subject(s) - chemistry , tetrapeptide , gastrin , calcium , peptide , binding site , stereochemistry , molecule , biological activity , ion , biophysics , crystallography , biochemistry , in vitro , secretion , organic chemistry , biology
The interaction of a series of biologically active gastrin fragments with calcium ions has been investigated by CD in trifluoroethanol. It was found that the gastrin octapeptide pGlu 10 ,Nle 15 ‐HG[10–17] binds one calcium ion per molecule. The hypothesis is made that the binding involves the C‐terminal, biologically important tetrapeptide. When the chain is elongated to the gastrin nonamer pGlu 9 ,Nle 15 ‐HG[9–17], a second binding site is available, which is most likely situated at the N‐terminal part of the molecule. Further elongation of the peptide chain up to the dodecapeptide pGlu 6 ,Nle 15 ‐HG[6–17] does not provide any additional binding site. Saturation of the two sites in the shorter peptides produces different changes in the chiroptical properties in the near‐ and far‐uv. As the chain is elongated, this difference tends to disappear. This result is consistent with an increased conformational order of the longer peptides. In the shorter fragments, the strength of this second binding is appreciably lower than that of the first, while in the longer peptides, the strength of the two bindings is comparable. On the assumption that the variation of the CD properties is proportional to the extent of binding, the constant for the binding of the second ion was determined to be of the order of 5 × 10 5 L/mol for the nonapeptide.